You'd expect as a Royal mother for Diana to be fairly strict and instil rules and traditions within her children, but as it turns out the People's Princess was a pretty fun mum who just loved her sons.

The brothers have previously admitted that Diana had a naughty streak and loved playing practical jokes on them - one of which left William feeling very embarrassed.

The Princess of Wales outside Wetherby School in London, with her sons William and Harry, April 1990) (Image: Jayne Fincher/Princess Diana Archive/Getty Images)

Read More

Speaking on a documentary about Princess Diana to mark the 20th anniversary of her death, named Diana, Our Mother: Her Life and Legacy, William and Harry recalled fond memories they had of their mother.

While looking through old family photos, they reminsced about their favourite childhood moments and spoke of how Diana loved to make mischief and "really enjoyed the laughter and the fun".

Apparently Diana was a practical joker and would send "rude" cards to William at school which he "dared not open" when teachers or other students were around.

William spoke of one prank in particular his mother played on him when he was becoming of age - and it's typical Diana!

William recalled: "There's a couple of memories I have that are particularly funny. Just outside this room where we are now, she organised, when I came home from school to have Cindy Crawford, Christy Turlington and Naomi Campbell waiting at the top of the stairs."

Read More

Princess Diana

"I was probably 12 or 13-year-old boy who had posters of them on my wall. And I went bright red and didn't quite know what to say and sort of fumbled, and I think I pretty much fell down the stairs on the way up."

"I was completely and utterly sort of awestruck. But that was a very funny memory that - that's lived with me forever about her loving and embarrassing and sort of, you know being - being the sort of the joker."

But that's not the only hilarious prank she played on the future King - when he turned 13 she ordered him a very rude birthday cake.

Her former head chef Darren McGrady previously recalled the hilarious when speaking to HELLO! Magazine.

Prince William arrives with Diana, Princess of Wales and Prince Harry for his first day at Eton College on September 16, 1995 in Windsor, England (Image: Anwar Hussein/Getty Images)